A friendly programming language from the future.

  • I’m currently learning functional languages and have only limited knowledge, but from what I’ve read now you are right. Throwing exceptions is pure, but catching them is impure.

    In this case I guess the printLine function can throw an exception therefore the calling function must be declared with Exception?

    • @robinm@programming.dev
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      21 year ago

      I would even have said that both throwing and catching should be pure, just like returning an error value/handling should be pure, but the reason for the throw/returning error itself is impure. Like if you throw and ioerror it’s only after doing the impure io call, and the rest of the error reporting/handling itself can be pure.

      • @Pipoca@lemmy.world
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        11 year ago

        Pure functions should be referentially transparent; you should be able to replace them with whatever value they evaluate to without changing the semantics of your code.

        Throwing is referentially impure: what value do you get from calling x => throw new RuntimeException()?

        Instead, functional languages prefer to return a tagged union of the value or the error.